Uv-curable epoxy acrylates

ABSTRACT

Epoxy acrylates of the formulae (A), (B) and epoxy acrylate mixtures comprising at least one of the compounds (A) or (B) are novel and find use in coating materials or adhesives featuring high UV stability

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Phase of International ApplicationPCT/EP2003/051057 filed Dec. 18, 2003 which designated the U.S. andwhich claims priority to Swiss Pat. App. No. 2161/02 filed Dec. 19,2002. The noted applications are incorporated herein by reference.

The present invention relates to novel epoxy acrylates and epoxyacrylate mixtures, to a process for the preparation and to the use ofthe epoxy acrylates of the Invention in coating materials or adhesiveswith high UV stability, and also to coating compositions and adhesivecompositions.

Epoxy acrylates are compounds prepared by reacting epoxides, eitherglycidyl ethers or cyclohexene oxides, with acrylic acid, that isproducing hydroxyacrylates.

By way of example the aromatic, industrially widespread BPA-DGE (e.gAraldit® GY240) or epoxyphenol novolaks (e.g. Araldit® EPN 1179) arereacted to the corresponding hydroxyacrylates. These are availablecommercially (from BASF, Cray Valley, UCB). Common to these products areviscosities of about 500–1000 Pas (25° C.) in the undiluted state. Forreasons of handling and processing they are generally diluted with alow-viscosity (5–50 mPas, 25° C.) acrylic monomer, such as HDDA, TMPTA,TPGDA, and other monomers known to the person skilled in the art.Radiation-induced free-radical curing of such products produces filmshaving good mechanical properties. Typical surface hardnesses (Persozhardness) of such “neat resin” homopolymers are 300–330 seconds.However, these high hardnesses are accompanied by Erichsen indentationvalues of <1 mm. Use is made generally of aromatic epoxy acrylates whenscratch resistance and chemical resistance are priorities. Aromaticcompounds are unsuitable in films exposed to weathering. In artificialweathering in a Weather-O-meter, for example, severe loss of gloss andyellowing are observed within 100 hours.

Epoxy acrylates made from linear aliphatic alcohols are also known.Commercially available examples include butanediol diglycidyl diacrylateand hexanediol diglycidyl diacrylate. They are notable for a lowviscosity (about 1 Pa*s, 25° C.) and solubility in water. Homopolymers,however, have weak mechanical properties. Neat resin Persoz hardnessesof around 50 seconds are commonplace.

The known epoxy acrylates, however, are not entirely satisfactory,particularly when not only outstanding mechanical properties but alsohigh UV stabilities are required. In many cases the known epoxyacrylates also have a considerable odour.

It was an object of the present Invention, therefore, to find odourlessepoxy acrylate compositions having both outstanding mechanicalproperties and high UV stabilities.

Surprisingly it has now been found that homopolymers of the novelcompound of the formula

meet the specified objectives. Also advantageous in the sense of theobject to be achieved is an epoxy acrylate mixture comprising A and B oran epoxy acrylate mixture which in addition to the compound of theformula A or B comprises at least one compound of the formula

The addition of compound D can be used to increase the network density.By adding compound E it is possible to set a favourable (reduced)working viscosity. Preferably, the epoxy acrylate mixtures according tothe invention contain as epoxy acrylates at least 30% by weight, morepreferably, at least 50% by weight, of compound A and/or B.

In this way compositions are achieved which have a solids content of100%, are odourless, and have good mechanical properties and high UVstabilities. The compositions of the invention display the statedadvantages when irradiated even with a low UV dose and are alsosuitable, when using corresponding monomers containing acceptor groups(such as NCO or COOR, for example), for the process known as dual cure,where an additional thermal cure is accomplished.

The novel compounds A and B can be prepared in a conventional manner byreacting the corresponding diglycidyl ethers with acrylic acid,preferably in a near-equinormal ratio of from 1:0.9 to 1:1.1. Furtherdetails and preferences are evident from the examples. Also of advantageis the simultaneous reaction of different glycidyl ethers with acrylicacid, leading directly to a composition of the Invention comprising atleast one compound A or B and also at least one further compound A to E.

The present invention provides for the use of the epoxy acrylates of theinvention in coating compositions and adhesive compositions.

The present invention further provides a radiation-curable coatingcomposition based on an epoxy acrylate binder containing from 5 to 90%by weight, preferably from 10 to 80% by weight, of the epoxy acrylate ofthe Invention, based on the total amount of binder.

The present invention further provides a radiation-curable adhesivecomposition based on an epoxy acrylate binder containing from 5 to 90%by weight, preferably from 10 to 80% by weight, of the epoxy acrylate ofthe invention, based on the total amount of binder.

The radiation-curable compositions of the Invention normally include aphotoinitiator. The photoinitiator content is preferably from 0.1 to 10%by weight and in particular from 1 to 8% by weight, based in each caseon the total amount of the epoxy acrylates. Suitable photoinitiators areknown to the person skilled in the art and some are also availablecommercially. Use may be made, for example, of the products availablecommercially under the name Irgacure® from Ciba Spezialitätenchemie. Inthe case of optional hybrid system compositions comprising an oxiranecompound, use is additionally made of initiators for photocationicpolymerization, which are likewise known to the person skilled in theart. Photoinitiators for cationic polymerization generate strongBrönsted acids when exposed to UV radiation and thereby Initiate thepolymerization of the epoxide groups. The compositions contain cationicphotoinitiators generally in amounts from 0.05 to 3% by weight, based onthe epoxy resin component. By way of example, cationic photoinitiatorshave as their general formula either S⁺(A₁A₂A₃)Q⁻ or I⁺(A₁A₂)Q⁻, inwhich A₁, A₂ and A₃ are identical or different aromatic radicals, whichmay be singly or multiply substituted and can contain heteroatoms, andQ⁻ is an anion such as BF₄ ⁻, PF₆ ⁻, AsF₆ ⁻, SbF₆ ⁻ or SnCl₆ ⁻, forexample. Examples of commercial products of the formula S⁺(A₁A₂A₃)Q⁻ areUVI-6974 (Q⁻=SbF₆ ⁻, Union Carbide), SP 170 (Q⁻=SbF₆ ⁻, Asahi DenkaKogyo K.K.) or K 185 (Q⁻=PF₆ ⁻, Sartomer). Examples of commercialproducts of the formula S⁺(A₁A₂A₃)Q⁻ are CD 1012 (Q⁻=SbF₆ ⁻, Sartomer),UV 9380C (Q⁻=SbF₆ ⁻, General Silicon) or CGI-552 (Q⁻=PF₆ ⁻, Ciba SC).The foregoing list is not exhaustive.

Besides the photoinitiators, suitable sensitizers can be used ineffective amounts.

The compositions of the invention are advantageously cured with actinicradiation, with UV radiation or with electron beams. Where appropriatethis can be carried out with or supplemented by actinic radiation fromother sources. In the case of electron beams it is preferred to operateunder an Inert gas atmosphere. This can be ensured, for example, bysupplying carbon dioxide and/or nitrogen directly to the surface of thecoating. In the case of UV radiation curing as well it Is possible tooperate under inert gas in order to prevent formation of ozone.

Curing with actinic radiation Is carried out using the conventional andknown radiation sources and optical auxiliary measures. Examples ofsuitable radiation sources are high-pressure or low-pressure mercuryvapour lamps, which are described for example in the brochures fromFusion Systems Inc. or Heraeus Holding GmbH. Their arrangement is knownIn principle and can be adapted to the circumstances of the workpieceand the process parameters. In the case of workpieces of complex shapethose regions not accessible to direct radiation (shadow regions), suchas cavities, folds and other structural undercuts, can be (partly) curedusing pointwise, small-area or all-round sources in conjunction with anautomatic movement means for the irradiation of cavities or edges.

During the curing of the film or films of the composition of theinvention that is or are present thereon using actinic radiation, thesubstrate can be at rest or can be guided past the radiation source atan appropriate speed. The UV lamps here are preferably of 100 to 200W/cm, more preferably from 120 to 190 W/cm and in particular from 140 to180 W/cm. Irrespective of whether the substrate is moved or is at rest,a radiation dose in the range from 50 to 6,000 mJ/cm², more preferablyfrom 50 to 2,000 mJ/cm², proves to be advantageous.

The compositions of the invention may further comprise the epoxy resins,preferably aliphatic epoxy resins, which are customary in epoxy resintechnology. Examples of such epoxy resins Include the following:

I) Polyglycidyl ethers or poly-(β-methylglycidyl)ethers, obtainable byreacting a compound having at least one, preferably two, free alcoholichydroxyl groups with epichlorohydrin or β-methylepichlorohydrin underalkaline conditions or in the presence of an acidic catalyst withsubsequent alkali treatment.

The glycidyl ethers of this type are derived for example from acyclicalcohols, such as ethylene glycol, diethylene glycol or higherpoly(oxyethylene)glycols, propane-1,2-diol or poly(oxypropylene)glycols,propane-1,3-diol, butane-1,4-diol, poly(oxytetramethylene)glycols,pentane-1,5-diol, hexane-1,6-diol, hexane-2,4,6-triol, glycerol,C₁₂₋₁₄OH (Araldit® DY-E) 1,1,1-trimethylolpropane, pentaerythritol,sorbitol, and also from polyepichlorohydrins. Other glycidyl ethers ofthis type are derived from cycloaliphatic alcohols, such as1,4-cyclohexanedimethanol, bis(4-hydroxycyclohexyl)methane,2,2-bis(4-hydroxycyclohexyl)-propane or tricyclodecanedimethanol.

II) Cycloaliphatic epoxy resins, such as bis(2,3-epoxycyclopentyl)ether,2,3-epoxycyclopentylglycidyl ether,1,2-bis(2,3-epoxycyclopentyloxy)ethane or the corresponding hydrogenatedbisphenol A diglycidyl ethers, bisphenol F diglycidyl ethers, or TCDdiglycidyl ethers.

Particularly preferred additional epoxy resins used are aliphatic epoxyresins such as trimethylolpropane triglycidyl ether and alsocycloaliphatic epoxy resins such as bis(2,3-epoxycyclopentyl)ether.

Besides the components named, the compositions of the invention may ofcourse comprise other components, which may differ according to thefield of use of the compositions, and which are known to the personskilled in the particular art field.

Coating compositions based on the epoxy acrylates may further comprise,for example, additives which are customary in the coatings industry, inthe amounts customary for those additives: they include lightstabilizers, curing accelerators, dyes, pigments, e.g. titanium dioxidepigment, devolatilizers, or else additional levelling agents.

Substrates suitable for coating include all surfaces amenable to coolingby actinic radiation. Examples include metals, plastics, wood, ceramic,stone, textile, leather, glass, including glass fibers, glass wool androck wool, mineral-bound and resin-bound building materials, such asplasterboard panels, cement slabs or roof tiles. Accordingly the coatingcomposition of the invention is suitable for applications such asautomotive finishing, and also in particular for the coating offurniture and for Industrial coating, including coil coating andcontainer coating. With the coating composition of the invention it isalso possible in particular to coat primed or unprimed plastics such as,for example, ABS, AMMA, ASA, CA, CAB, EP, UF, CF, MP, MPF, PF, PAN, PA,PE, HDPE, LDPE, LLDPE, UHMWPE, PET, PMMA, PP, PS, SB, PUR, PVC, RF, SAN,PBT, PPE, POM, PUR-RIM, SMC, BMC, PP-EPDM and UP (abbreviationsaccording to DIN 7728T1).

Unless indicated otherwise, parts and percentages in the examples and inthe remainder of the description are by weight As common In thechemistry of epoxy compounds and especially for compounds produced on anindustrial scale, the structural formulae are idealized and representthe largely predominant structure present.

EXAMPLES Example 1

Preparation of

A mixture of 300 g of hydrogenated bisphenol A diglycidyl ether (1.275eq of epoxide) and 0.39 g of di-tert-butyl-para-cresol (DBPC) is heatedto 95° C., stirred and saturated with air using a gas introduction frit.Added dropwise to this mixture over the course of 22 minutes is asolution of 0.775 g of Cr^(III) isooctanoate (Hexcem) in 22 ml ofacrylic acid. The remaining 64 ml of acrylic acid (in all 87.3 g, 95 eq%) are metered in over 40 minutes. After a further five hours ofstirring at 100° C. the mixture Is cooled to room temperature. Thehomogeneous, transparent, slightly greenish liquid has a viscosity of 48Pa*s (25° C.), an epoxide content of 0.45 eq/kg and an acid content of0.07 eq/kg.

Compounds A, B and E are prepared In precise analogy. The details of thecompounds are summarized In Table 1.

Example 2

Preparation of a Mixture of Compounds A, D and E

A mixture of 150 g of tricyclodecanedimethanol diglycidyl ether (0.824eq of epoxide), 100 g of triglycidyl isocyanurate (0.962 eq of epoxide),50 g of DY-E (0.159 eq of epoxide) and 0.44 g ofdi-tert-butyl-para-cresol (DBPC) is heated to 95° C., stirred andsaturated with air using a gas Introduction fit. Added dropwise to thismixture over the course of 14 minutes is a solution of 0.880 g ofCr^(III) isooctanoate (Hexcem) in 24 ml of acrylic add. The remaining 94ml of acrylic acid (in all 140.2 g, 95 eq %) are metered In over thecourse of 66 minutes. After a further five hours of stirring at 100° C.the mixture Is cooled to room temperature. The homogeneous, transparent,slightly greenish liquid has a viscosity of 34 Pas (25° C.), an epoxidecontent of 0.30 eq/kg and an acid content of 0.1 eq/kg.

TABLE 1 Compound A B C A + D + E E Glycidyl Tricyclodecane- HydrogenatedHydrogenated Tricyclodecane- DY-E⁴⁾ ether dimethanol BPF-DGE²⁾ BPA-DGE³⁾dimethanol DGE¹⁾ DGE + TGIC + DY-E Method Example 1 Example 1 Example 1Example 2 Example 1 Appearance homogeneous, homogeneous, homogeneous,homogeneous, homogeneous, of epoxy transparent, transparent,transparent, transparent, transparent, acrylate slightly slightlyslightly slightly slightly greenish liquid greenish liquid greenishliquid greenish liquid greenish liquid Viscosity⁵⁾ 17 Pa*s (25° C.) 22.4Pa*s (25° C.) 48 Pa*s (25° C.) 34 Pa*s (25° C.) 34 mPa*s (25° C.) EPcontent⁶⁾ 0.13 eq/kg 0.273 eq/kg 0.45 eq/kg 0.3 eq/kg 0.445 eq/kg COOHcontent⁷⁾ 0.02 eq/kg 0.12 eq/kg 0.07 eq/kg 0.1 eq/kg 0.14 eq/kg¹⁾prepared by reacting tricyclodecanedimethanol with epichlorohydrin²⁾prepared by reacting bisphenol F diglycidyl ether (Araldit ® GY285Vantico) with H₂ ³⁾prepared by reacting bisphenol A diglycidyl ether(Araldit ® GY240 Vantico) with H₂ ⁴⁾monoglycidyl ether of the alcoholmixture nC₁₂OH + nC₁₃OH + nC₁₄OH ⁵⁾cone and plate Brookfield viscometer,measurements with cone 06, 50 rpm at 25.0° C. ⁶⁾tetraethylammoniumbromide/HOAc, then 0.1N HClO₄ titration ⁷⁾0.1N KOH titration

Examples 3–5

The table below symbolizes the investigations and the coatings obtainedon the epoxy acrylates of the invention.

TABLE 2 Example 3 4 5 Comp. 1 Comp. 2 Epoxy A B A + D + LR8713**LR8765*** acrylate E* Odour none none none solvent strong BuOAc Doserequired 41 65 26 104 26 to attain acetone resistance¹⁾ Persoz 323 296298 175 56 hardness ²⁾ Erichsen 3.4 2.9 0.6 1.8 3.8 indentation ³⁾ Gloss1000^(4a)) 1200^(4a)) n.d. 200^(4b)) Film retention none^(4a))none^(4a)) none^(4a)) about detached Yellowing 150^(4b)) within 100h^(4b)) Dose needed 115 191 96 96 96 to attain scratch resistance⁵⁾ *inaccordance with Example 2 **aromatic epoxy acrylate (BASF) ***aliphaticepoxy acrylate (BASF) n.d.: not determined ¹⁾ . . . copper-laminatedcircuit board coated with undiluted resin containing 4% Irgacure ® 500(Ciba Spezialitätenchemie) in 100 μm film thickness. Covered over withquartz glass web (11 discrete transmissions) and exposed using undopedhigh-pressure mercury vapour lamp with a UV dose of 1132 mJ/cm².Developed in acetone for 3 minutes and last undetached layer convertedto dose. Result reported in mJ/cm². ²⁾ . . . Persoz glass plate coatedwith undiluted resin containing 4% Irgacure ® 500 (CibaSpezialitätenchemie) in 100 μm film thickness. Exposed using undopedhigh-pressure mercury vapour lamp with UV dose of 5560 mJ/cm². Persozpendulum hardness determined in accordance with DIN EN ISO 1522 (averagefrom two or more measurements). Result reported in seconds. ³⁾ . . .Bonder 26 0 60C zinc-phosphatized steel plate coated with undilutedresin containing 4% Irgacure ® 500 (Ciba Spezialitätenchemie) in 50 μmfilm thickness. Exposed using undoped high-pressure mercury vapour lampwith UV dose of 5560 mJ/cm². Erichsen indentation determined inaccordance with DIN EN ISO 1520 (average from two or more measurements).Result reported in mm. ^(4a);4b)). . . Untreated aluminium plates coatedwith white-pigmented resin containing 1% Irgacure ® 819 (CibaSpezialitätenchemie) in 50 μm film thickness. Exposed usinggallium-doped high-pressure mercury vapour lamp with a UV dose of 1132mJ/cm². ^(4a)). . . In WOM (Weather-O-matic) unit under standardconditions. Result reported in hours. ^(4b)). . . In QUV units,irradiated with UV. Result reported in hours. ⁵⁾ . . . Black-paintedcard coated with undiluted resin containing 4% Irgacure 500 ® (CibaSpecialties) in 50 μm film thickness. Belt speed during irradiation withundoped high-pressure mercury vapour lamp increased until slightscratching with fingernail leaves a track. Result reported in mJ/cm²(belt speed).

Gloss Determination:

The gloss is determined in accordance with ISO 2813 standard.

1. An epoxy acrylate selected from the group consisting of formula (A)


2. An epoxy acrylate mixture comprising at least two different epoxyacrylates selected from the group consisting of formula (A)

with the proviso that at least one epoxy acrylate is the epoxy acrylateof formula A or formula B.
 3. The epoxy acrylate mixture according toclaim 2 comprising at least 30% by weight of the epoxy acrylate offormula A and/or formula B.
 4. The epoxy acrylate mixture according toclaim 2 comprising at least 50% by weight of the epoxy acrylate offormula A and/or formula B.
 5. A radiation-curable compositioncomprising an epoxy acrylate binder containing 5 to 90% by weight basedon the total amount of binder of an epoxy acrylate selected from thegroup consisting of formula (A)


6. A radiation-curable composition comprising an epoxy acrylate bindercontaining 5 to 90% by weight based on the total amount of binder of anepoxy acrylate mixture comprising at least two different epoxy acrylatesselected from the group consisting of formula (A)

with the proviso that at least one of the epoxy acrylates is the epoxyacrylate of formula A or formula B.
 7. A method for coating a substrateby applying the radiation-curable composition according to claim 5 toone or more surfaces of the substrate and curing the composition withradiation.
 8. A method for coating a substrate by applying theradiation-curable composition according to claim 6 to one or moresurfaces of the substrate and curing the composition with radiation. 9.A method for preparing an epoxy acrylate according to claim 1 byreacting acrylic acid with corresponding diglycidyl ether in anear-equinormal ratio of from 1:0.9 to 1:1.1.
 10. A method for preparingan epoxy acrylate mixture according to claim 2 by reacting acrylic acidwith corresponding diglycidyl ether in a near-equinormal ratio of from1:0.9 to 1:1.1.